local-time: the panel in the container's zone, named on Settings

Agreed by the owner on 2026-10-13 (the local day, no "UTC" beside a
time); the zone is the container's TZ in .env and Settings only shows it,
his "Да" of 2026-10-17. Mockups c205106.

Every time the panel shows is formatted in time.Local and says no zone:
the logs' Time and the DMARC Received columns, a message's timeline,
Overview's "Updated", Health's certificate and renewal, the filter lists,
DMARC reports and windows, the auto limit's last recalculation. Stored
instants stay UTC. The days counted are the zone's: delivery_log_days and
sender_check_days key their rows by the local date, the sender check cuts
downtime at local midnights (byDay), the log filters' days run from local
midnight to local midnight. Notification mail and the test message write
the zone's abbreviation after a time - they are read away from the panel.
DMARC's one-day window label stays the reporter's (UTC) day.

Settings box 05, Time zone, read-only: the name (UTC without TZ), its
offset, and a TZ the image cannot load said to leave the times in UTC
(time/zoneinfo_unix.go, initLocal) rather than named. TZ is passed by the
compose file ("${TZ:-}"), in .env.example and the guide's table; tzdata is
named in the image (supervisor's python3.13 brings it today). Postfix
takes TZ through import_environment, so mail.log's stamps are the same
zone, which closes the trap the roadmap wrote down: the tailer has always
read them in time.Local.

Tests: a TestMain runs view, handlers, store and cmd/panel in UTC whatever
the machine's zone (as logtail's); TestSettingsShowsTheTimeZone,
TestTimesAreTheContainersZone, TestByDayInTheContainersZone, a Moscow day
in TestQueryInboundSpamFilters; envdoc's pattern takes two-letter names.
e2e time_zone_is_the_containers recreates the stand with
TZ=Europe/Moscow: date says MSK, Settings names the zone and UTC+03:00, a
test message's page gives its time and its mail.log lines in Moscow's.
go vet + go test (26 packages) and make e2e on the test server for this
tree.

Docs: guide (§ Settings, the TZ row, the days of Health and the logs),
architecture, schema-migrations, help (word for word with the mockup),
CHANGELOG [Unreleased] § Added, roadmap row done with the decision.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/store/sendercheck.go

@@ -26,7 +26,7 @@ const (
 
 // Settings keys of the sender check's statistics.
 const (
-	// settingSenderCheckSince is the first UTC day the statistics cover.
+	// settingSenderCheckSince is the first day (of the container's zone) the statistics cover.
 	settingSenderCheckSince = "sender_check_since"
 	// settingSenderCheckDeferredAt is when a message was last deferred because
 	// the check did not answer (RFC3339 UTC).
@@ -66,7 +66,7 @@ func (s *Store) StartSenderCheckStats(now time.Time) error {
 	if err != nil || v != "" {
 		return err
 	}
-	return s.SetSetting(settingSenderCheckSince, now.UTC().Format(dayLayout))
+	return s.SetSetting(settingSenderCheckSince, now.Local().Format(dayLayout))
 }
 
 // AddSenderCheckDown adds to the day of at the time the panel did not answer
@@ -81,7 +81,7 @@ func (s *Store) AddSenderCheckDown(at time.Time, d time.Duration, estimated bool
 		`INSERT INTO sender_check_days (day, down_seconds, estimated) VALUES (?, ?, ?)
 		 ON CONFLICT (day) DO UPDATE SET down_seconds = down_seconds + excluded.down_seconds,
 			estimated = MAX(estimated, excluded.estimated)`,
-		at.UTC().Format(dayLayout), secs, estimated,
+		at.Local().Format(dayLayout), secs, estimated,
 	)
 	if err != nil {
 		return fmt.Errorf("sender check downtime: %w", err)
@@ -114,7 +114,7 @@ func (s *Store) AddSenderCheckDeferred(at time.Time, n int64, place string, mess
 	if _, err := tx.Exec(fmt.Sprintf(
 		`INSERT INTO sender_check_days (day, %[1]s) VALUES (?, ?)
 		 ON CONFLICT (day) DO UPDATE SET %[1]s = %[1]s + excluded.%[1]s`, column),
-		at.UTC().Format(dayLayout), n,
+		at.Local().Format(dayLayout), n,
 	); err != nil {
 		return fmt.Errorf("sender check deferred: %w", err)
 	}
@@ -163,7 +163,7 @@ func (s *Store) SenderCheckDeferredAt() (time.Time, error) {
 // SenderCheckStats sums the days up to now: today, the last 30 days and the
 // last 12 months, each including today.
 func (s *Store) SenderCheckStats(now time.Time) (SenderCheckStats, error) {
-	now = now.UTC()
+	now = now.Local()
 	var out SenderCheckStats
 	sum := func(days int) (SenderCheckTotals, error) {
 		var secs, deferred, messages, estimated int64
@@ -193,7 +193,7 @@ func (s *Store) SenderCheckStats(now time.Time) (SenderCheckStats, error) {
 	if err != nil {
 		return out, err
 	}
-	out.Since, _ = time.Parse(dayLayout, since)
+	out.Since, _ = time.ParseInLocation(dayLayout, since, time.Local)
 	deferredAt, err := s.GetSetting(settingSenderCheckDeferredAt)
 	if err != nil {
 		return out, err
@@ -205,7 +205,7 @@ func (s *Store) SenderCheckStats(now time.Time) (SenderCheckStats, error) {
 // PruneSenderCheckDays deletes the days older than a year.
 func (s *Store) PruneSenderCheckDays(now time.Time) error {
 	_, err := s.db.Exec(`DELETE FROM sender_check_days WHERE day < ?`,
-		now.UTC().AddDate(0, 0, -senderCheckKeepDays).Format(dayLayout))
+		now.Local().AddDate(0, 0, -senderCheckKeepDays).Format(dayLayout))
 	if err != nil {
 		return fmt.Errorf("prune sender check days: %w", err)
 	}